1. Field of the Invention
Disclosed herein is a signal processing apparatus and method for removing a reflected wave generated by a robot platform.
2. Description of the Related Art
Recently, much interest has been focused on industries for intelligent robots that can interact with human beings. It is important that a robot detect the exact position of a robot user who is a conversational partner for Human-Robot Interaction (HRI). Therefore, a technique for detecting the direction of a sound source using an acoustic sensor is one of essential techniques for HRI.
The related art technique for detecting the direction of a sound source includes a method using Time Delay Of Arrivals (TDOA), a method using a Head-Related Transfer Function (HRTF) database of a robot platform, a beamforming method using a plurality of microphone arrays, and the like.
The method using the TDOA is a method for estimating the direction of a sound source using a delay time at which a sound of a speaker arrives at each sensor. Since the method has a simple algorithm and a small amount of calculation, it is frequently used for estimating the position of a sound source in real time. However, when there is a constraint that a microphone should be disposed in a narrow area such as each user's ear, i.e., when the distance between the microphones is shortened, the method is disadvantageous in that estimation resolution is reduced. When only two microphones are used in a narrow area, a sound source has the same delay time at two positions on a two-dimensional plane, and therefore, front-back confusion occurs. That is, if the position of a sound source is estimated based on only the delay time difference when only the two microphones are used, front-back discrimination is impossible.
The method using the HRTF is a method for detecting the direction of a sound source using information on the magnitude and phase of an HRTF. The method is similar to the sound source direction detecting method of human beings, but a change in transfer function, caused by an external ear, is shown in frequency domain higher than the sound frequency area (˜4 kHz). Therefore, the method is disadvantageous in that a relatively large-sized artificial ear is necessarily used and the amount of database for sound source direction detection is increased.
The beamforming method is a method for matching a vector of a virtual sound source to a position vector of a real sound source while rotating the vector of the virtual sound source. In the beamforming method, an array having a plurality of fixed sensors is necessarily used. When a plurality of microphones are used, a high-end hardware for signal processing is required, and the amount of data to be processed is increased. Therefore, the beamforming method is disadvantageous in that it is unsuitable for detecting the direction of a sound source in real time.
Artificial ears manufactured using the related art techniques are influenced by a robot platform, i.e., reflected microwaves measured from a microphone used in sound source direction detection, and therefore, it is difficult to detect the exact direction of a sound source. Generally, the auditory structure of a robot has a shape suitable for the shape of a robot platform. However, when a new robot is developed, a robot acoustic system for eliminating the influence of reflected waves is necessarily developed accordingly.